This series consists of materials related to individual faculty members and other individuals with ties to the Department of Physics, usually as a guest lecturer. Materials include original correspondence between prominent physicists from within and outside the Columbia University community, photographs, negatives, notes, and lecture announcements. Files are arranged alphabetically by last name of the individual. Much of the correspondence from these individuals is with Dean George B. Pegram. Of particular interest are two notebooks of George B. Pegram from when he was a student at Columbia in 1899 as well a notebook of lectures by Professor McCullogh as transcribed by Peter A. Jay in 1862. Files containing correspondence have date ranges noted; those with just photographs are almost always undated.